Localized wireless networking for sensing and/or control purposes is becoming increasingly common. Fairly large area installations may use a mesh or other nodal wireless network topology for communications. In a wireless network having radio-frequency (RF) nodes, each node typically includes a receiver and transmitter, sometimes referred to collectively as a transceiver, offering capabilities for receiving and sending digital information over radio signals. The device at each node of the network may include a sensor and/or a controlled element, such as a light source. Where operation of the controllable elements is perceptible by a person in a location or premises served by the system, it may be desirable for some or all of the nodes to execute a common control operation (e.g. turn all lights On or turn all lights Off) sufficiently close in time that the perceptible operations of the devices at the nodes appear to be simultaneous to any person who may observe the nodes as they execute the control operation in common.
In one example of RF-networked luminaires, approximately 400 luminaires in a big-box store interior are to be turned on, that is, a Lights On command is to be received and executed by all the luminaires. If the command is propagated node-to-node by normal network procedures, hopping opportunistically through the network (e.g. through a routing mesh network), and if the command is furthermore executed by each luminaire upon receipt at each different node, then the lights will tend to turn on in a perceptibly non-synchronous manner: an erratic wave of turn-ons will propagate across the ceiling. This distracting outcome is termed the “popcorn effect” by analogy to the unpredictable, asynchronous popping of kernels in a popper. The popcorn effect can create unwelcome visual effects for any kind of perceptible light adjustment (on, off, dimming, color change). In some applications (e.g., stage lighting, studio lighting, TV and movie lighting), perceptible pop-corning may be completely unacceptable. Older lighting systems avoided pop-corning by direct hard-wiring of all luminaires to a power source. Flipping a switch sends the “command” (power) to all luminaires simultaneously. However, such technique does not assure substantially simultaneous command execution for network-disseminated digital commands in a wireless luminaire system e.g. that uses a wireless nodal network for command communication. Thus, there is a need for a method of assuring command execution by devices in a nodal network that will be at least sufficiently close in time to appear simultaneous to a person observing execution of the command at a number of nodes of the system.